Phosphor based light sources having a non-planar short pass reflector and method of making

ABSTRACT

A light source includes an LED that emits excitation light, a layer of phosphor material positioned to receive the excitation light, the phosphor material emitting visible light when illuminated with the excitation light, and a non-planar flexible multilayer reflector that transmits the excitation light and reflects visible light. The non-planar flexible multilayer reflector is positioned between the LED and the layer of phosphor material.

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. ProvisionalApplication Nos. 60/443,274, 60/443,232, and 60/443,235 all filed 27Jan. 2003, and all incorporated by reference herein.

RELATED PATENT APPLICATIONS

[0002] The following co-owned and concurrently filed U.S. patentapplications are incorporated herein by reference: “PHOSPHOR BASED LIGHTSOURCES HAVING A POLYMERIC LONG PASS REFLECTOR”, Attorney Docket No.58389US004; “METHODS OF MAKING PHOSPHOR BASED LIGHT SOURCES HAVING ANINTERFERENCE REFLECTOR”, Attorney Docket No. 58390US004; “PHOSPHOR BASEDLIGHT SOURCE COMPONENT AND METHOD OF MAKING”, Attorney Docket No.59414US002; “PHOSPHOR BASED LIGHT SOURCE HAVING A FLEXIBLE SHORT PASSREFLECTOR”, Attorney Docket No. 59415US002; “PHOSPHOR BASED LIGHTSOURCES HAVING A NON-PLANAR LONG PASS REFLECTOR”, Attorney Docket No.59416US002; and “PHOSPHOR BASED LIGHT SOURCES HAVING A NON-PLANAR LONGPASS REFLECTOR AND METHOD OF MAKING”, Attorney Docket No. 59417US002.

FIELD OF THE INVENTION

[0003] The present invention relates to light sources. Moreparticularly, the present invention relates to light sources in whichlight emitted from a light emitting diode (LED) impinges upon andexcites a phosphor material, which in turn emits visible light.

DISCUSSION

[0004] White light sources that utilize LEDs in their construction canhave two basic configurations. In one, referred to herein as directemissive LEDs, white light is generated by direct emission of differentcolored LEDs. Examples include a combination of a red LED, a green LED,and a blue LED, and a combination of a blue LED and a yellow LED. In theother basic configuration, referred to herein as LED-excitedphosphor-based light sources (PLEDs), a single LED generates a beam in anarrow range of wavelengths, which beam impinges upon and excites aphosphor material to produce visible light. The phosphor can comprise amixture or combination of distinct phosphor materials, and the lightemitted by the phosphor can include a plurality of narrow emission linesdistributed over the visible wavelength range such that the emittedlight appears substantially white to the unaided human eye.

[0005] An example of a PLED is a blue LED illuminating a phosphor thatconverts blue to both red and green wavelengths. A portion of the blueexcitation light is not absorbed by the phosphor, and the residual blueexcitation light is combined with the red and green light emitted by thephosphor. Another example of a PLED is an ultraviolet (UV) LEDilluminating a phosphor that absorbs and converts UV light to red,green, and blue light.

[0006] Advantages of white light PLEDs over direct emission white LEDsinclude better color stability as a function of device aging andtemperature, and better batch-to-batch and device-to-device coloruniformity/repeatability. However, PLEDs can be less efficient thandirect emission LEDs, due in part to inefficiencies in the process oflight absorption and re-emission by the phosphor.

[0007] A white light PLED can comprise a UV emitting semiconductor die(chip) in a reflective heat sink. The reflective heat sink can alsoserve to partially collimate the UV light. The UV light illuminates theunderside of a phosphor-containing layer, which absorbs at least aportion of the UV light and emits light at multiple wavelengths in thevisible region to provide a source appearing substantially white to theordinary observer. FIG. 1 shows one configuration of such a PLED 10. ThePLED includes a semiconducting LED 12 mounted in a well of anelectrically conductive heat sink 14 that also reflects some of thelight emitted from LED 12 toward a phosphor-reflector assembly 16. Theassembly 16 can reside in an optically transparent potting material 18which can be shaped to provide a lens feature 20 to tailor the lightemitted by PLED 10. The phosphor assembly 16 is shown in greater detailin FIG. 2. The phosphor is formed into a layer 22 from a combination ofone or more phosphor materials mixed with a binder. A long-pass (LP)reflector 24, that reflects the UV excitation light but transmits thevisible emitted light, can be applied to the top surface of phosphorlayer 22. A short-pass (SP) reflector 26, that reflects visible lightbut transmits UV light, can be applied to the bottom of layer 22.

[0008] The optimum thickness of the phosphor layer for a given phosphorconcentration is a compromise between efficiently absorbing the UV light(favoring an optically thick phosphor layer) and efficiently emittingvisible light (favoring an optically thin phosphor layer). Further,since the intensity of UV light is greatest at the bottom of phosphorlayer 22, and useful light is being extracted from the top of phosphorlayer 22, increasing the thickness of phosphor layer 22 above theoptimum thickness will rapidly reduce overall PLED output andefficiency.

[0009] The presence of LP reflector 24 and SP reflector 26 can enhancethe efficiency of PLED 10. The LP reflector 24 reflects the UV lightthat is not absorbed by phosphor layer 22, and that would otherwise bewasted, back onto the phosphor layer 22. This increases the effectivepath length of the UV light through the phosphor layer, increasing theamount of UV light absorbed by the phosphor for a given phosphor layerthickness. The optimum phosphor layer thickness can thus be reducedcompared to a construction without LP reflector 24, increasing theefficiency of light generation.

[0010] Another significant loss in the PLED is due to the directionallyuncontrolled generation of light in the phosphor layer, resulting inhalf of the visible light generated in phosphor layer 22 being directedback towards the LED. Some of this light can be captured by reflectionoff the sloped walls of the heat sink, but much of the light isscattered, absorbed, or reduced in quality. This loss can be reduced byplacing SP reflector 26 as shown between LED 12 and phosphor layer 22.

[0011] It would be advantageous to even further enhance the efficiencyof PLED constructions. It would also be advantageous to simplify andreduce the cost of manufacture of PLEDs.

BRIEF SUMMARY

[0012] The present application discloses PLEDs that utilize polymermultilayer optical films for the filtering components, i.e., the LP andSP reflectors. The multilayer optical films include individual opticallayers, at least some of which are birefringent, arranged into opticalrepeat units through the thickness of the film. Adjacent optical layershave refractive index relationships that maintain reflectivity and avoidleakage of p-polarized light at moderate to high incidence angles. TheSP reflector comprises optical repeat units having a thickness gradientthat produces a reflection band positioned to reflect visible lightemitted by the phosphor and transmit UV excitation light. The LPreflector comprises optical repeat units having a different thicknessgradient that produces a reflection band positioned to reflect the UVexcitation light and transmit the visible light emitted by the phosphor.As a component of the PLED, the polymer multilayer optical film(s) canhave a flat configuration or at least one can be embossed or otherwiseshaped to be curved, whether in the shape of a sphere, paraboloid,ellipsoid, or other shape.

[0013] Methods of manufacturing PLEDs are disclosed, which methodsinclude forming a sheet material that includes at least one polymermultilayer optical film and a phosphor layer. In some cases the phosphorcan be sandwiched between two polymer multilayer optical films: one SPreflector, and one LP reflector. In other cases the phosphor layer canbe applied to only one polymer multilayer optical film. The polymermultilayer optical film(s) and phosphor layer form a phosphor-reflectorassembly. Individual pieces of the phosphor-reflector assembly can becut from the sheet material and subsequently immersed in a transparentpotting material or injection-molded to form a first optical componentwhich is then coupled to a separately manufactured LED component. Thesheet material can include a carrier film to hold and store thephosphor-reflector assembly pieces in a convenient roll form untilneeded. The PLED can be made by joining a lower portion comprising theLED to an upper portion comprising a phosphor-reflector assembly. Alsoin some cases the sheet material can be embossed

[0014] The present specification discloses PLED embodiments in which acurved LP reflector is spaced apart from the phosphor layer, or at leastfrom a central bright portion thereof, so that any UV excitation lightnot absorbed by the phosphor layer will impinge on the LP reflector overa limited range of incidence angles and be more efficiently reflectedback onto the phosphor layer.

[0015] The present application discloses PLED embodiments that utilizean air gap proximate at least one of the multilayer optical films andthe phosphor layer to promote total internal reflection.

[0016] The present application discloses PLED embodiments that utilizecombinations of non-imaging concentrator elements to enhance theperformance of the LP and/or SP reflector.

[0017] The present application also discloses PLED embodiments in whichthe LED, the LP reflector, and the phosphor layer are arranged such thatexcitation light from the LED is reflected directly onto a front majorsurface of the phosphor layer.

[0018] These and other aspects of disclosed embodiments will be apparentfrom the detailed description below. In no event, however, should theabove summaries be construed as limitations on claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Throughout the specification, reference is made to the appendeddrawings, where like reference numerals designate like elements, andwherein:

[0020]FIG. 1 is a schematic sectional view of a LED-excitedphosphor-based light source (PLED);

[0021]FIG. 2 is a sectional view of a phosphor-reflector assembly usedin the source of FIG. 1;

[0022]FIG. 3 depicts a roll comprising a phosphor-reflector assembly insheet form and subdivided into individual pieces;

[0023]FIG. 4 is a schematic sectional view illustrating individualpieces of the phosphor-reflector assembly on a carrier film;

[0024] FIGS. 5-7 are schematic sectional views of alternative PLEDconstructions;

[0025]FIG. 8 depicts a portion of still another PLED construction;

[0026]FIG. 9 is a schematic sectional view of still another PLEDconstruction;

[0027]FIG. 10 is a schematic side view of another PLED construction thatutilizes front surface illumination, as does the embodiment of FIG. 9;

[0028]FIG. 11 is a schematic side view of a PLED construction that makesuse of an arrangement of nonimaging concentrators; and

[0029]FIG. 12 is a close-up view of a portion of FIG. 11.

[0030] FIGS. 13-17 are schematic sectional views of other embodiments ofPLED constructions;

[0031] FIGS. 18-21 are sectional views of other embodiments of PLEDconstructions;

[0032]FIG. 22 is a graph of a light intensity spectrum of Examples 1 and2;

[0033]FIG. 23 is a graph of a light intensity spectrum of Examples 3, 4,and 5;

[0034]FIG. 24 is a graph of a light intensity spectrum of Examples 6, 7,and 8; and

[0035]FIG. 25 is a graph of a light intensity spectrum of Examples 9 and10.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0036] While the use of one or both of LP reflector 24 and SP reflector26 as shown in FIGS. 1-2 can improve system efficiency, the improvementis limited due to certain reflectors' poor spectral selectivity and poorreflectivity at oblique angles of incidence. LP mirrors or filters basedon scattering processes can achieve relatively constant performance as afunction of incidence angle, but have poor spectral selectivity. LP andSP mirrors constructed from an inorganic dielectric material stack canhave good spectral selectivity over a narrow range of incidence angles,but suffer from spectral blue-shifts with increasing incidence angle andlow reflectivity (high transmission) of p-polarized light at moderate tohigh incidence angles. Since phosphor particles scatter the UVexcitation light, and emit their own light over a wide range of angles,conventional LP and SP mirrors are not highly effective in managinglight within the phosphor-reflector assembly.

[0037] The performance of PLEDs can be increased by using polymericmultilayer optical films, i.e., films having tens, hundreds, orthousands of alternating layers of at least a first and second polymermaterial, whose thicknesses and refractive indices are selected toachieve a desired reflectivity in a desired portion of the spectrum,such as a reflection band limited to UV wavelengths or a reflection bandlimited to visible wavelengths. See, for example, U.S. Pat. No.5,882,774 (Jonza et al.). Although reflection bands produced by thesefilms also experience a blue-shift with incidence angle similar to theblue-shift associated with stacks of inorganic isotropic materials, thepolymeric multilayer optical films can be processed so that adjacentlayer pairs have matching or near-matching, or deliberately mismatchedrefractive indices associated with a z-axis normal to the film such thatthe reflectivity of each interface between adjacent layers, forp-polarized light, decreases slowly with angle of incidence, issubstantially independent of angle of incidence, or increases with angleof incidence away from the normal. Hence, such polymeric multilayeroptical films can maintain high reflectivity levels for p-polarizedlight even at highly oblique incidence angles, reducing the amount ofp-polarized light transmitted by the reflective films compared toconventional inorganic isotropic stack reflectors. In order to achievethese properties, the polymer materials and processing conditions areselected so that, for each pair of adjacent optical layers, thedifference in refractive index along the z-axis (parallel to thethickness of the film) is no more than a fraction of the refractiveindex difference along the x- or y- (in-plane) axes, the fraction being0.5, 0.25, or even 0.1. Alternatively, the refractive index differencealong the z-axis can be opposite in sign to the in-plane refractiveindex differences.

[0038] The use of polymeric multilayer optical films also makesavailable a variety of new PLED embodiments and methods of constructiondue to the flexibility and formability of such films, whether or notthey also have the refractive index relationships referred to above. Forexample, polymeric multilayer optical film can be permanently deformedby embossing, thermoforming, or other known means to have a3-dimensional shape such as a portion of a paraboloid, a sphere, or anellipsoid. See generally published application U.S. Ser. No.2002/0154406 (Merrill et al.). See also U.S. Pat. No. 5,540,978(Schrenk) for additional polymeric multilayer film embodiments. Unlikeconventional inorganic isotropic stacks, which are normally vapordeposited layer-by-layer onto a rigid, brittle substrate, polymericmultilayer optical films can be made in high volume roll form, and canalso be laminated to other films and coated, and can be die cut orotherwise subdivided into small pieces for easy incorporation into anoptical system such as a PLED as further explained below. Suitablemethods of subdividing polymeric multilayer optical film are disclosedin pending U.S. application Ser. No. 10/268,118, filed Oct. 10, 2002.

[0039] A wide variety of polymer materials are suitable for use inmultilayer optical films for PLEDs. However, particularly where the PLEDcomprises a white-light phosphor emitter coupled with a UV LEDexcitation source, the multilayer optical film preferably comprisesalternating polymer layers composed of materials that resist degradationwhen exposed to UV light. In this regard, a particularly preferredpolymer pair is polyethylene terephthalate(PET)/co-polymethylmethacrylate (co-PMMA). The UV stability of polymericreflectors can also be increased by the incorporation of non-UVabsorbing light stabilizers such as hindered amine light stabilizers(HALS). In some cases the polymeric multilayer optical film can alsoinclude transparent metal or metal oxide layers. See e.g. PCTPublication WO 97/01778 (Ouderkirk et al.). In applications that useparticularly high intensity UV light that would unacceptably degradeeven robust polymer material combinations, it may be beneficial to useinorganic materials to form the multilayer stack. The inorganic materiallayers can be isotropic, or can be made to exhibit form birefringence asdescribed in PCT Publication WO 01/75490 (Weber) and thus have thebeneficial refractive index relationships that yield enhancedp-polarization reflectivity as described above. However, in most casesit is most convenient and cost effective for the multilayer optical filmto be substantially completely polymeric, free of inorganic materials.

[0040]FIG. 3 depicts a roll of sheet material 30, which materialcomprises at least one polymeric multilayer optical film and asubstantially uniform phosphor layer applied to the multilayer opticalfilm by a coating operation. The sheet material can also comprise asecond polymeric multilayer optical film applied in such a way that thephosphor layer is sandwiched between the first and second polymericmultilayer optical film, as seen in FIG. 2. Additional layers andcoatings providing desired mechanical, chemical, and/or opticalproperties can also be included. See U.S. Pat. No. 6,368,699 (Gilbert etal.). The sheet material 30 also preferably includes a carrier film. Thesheet material is kiss-cut by mechanical means such as a knife,precision die cutting, or by scanning laser radiation as described inthe pending '118 application referred to above. The kiss-cut linesdefine discrete pieces 32 of the sheet material, but exclusive of thecarrier film which remains intact. The pieces 32 can have across-sectional construction similar to that shown in FIG. 2, and can beof arbitrarily small size. They are conveniently carried by theunderlying carrier film 34 as shown in FIG. 4. During production of thePLEDs—and independent of the construction of the LED source—pieces 32can be removed from the carrier film and placed in individual molds towhich potting material is, or was previously, added, thus forming PLEDsas depicted in FIG. 1 but wherein the reflector components use polymericmultilayer optical films.

[0041] FIGS. 5-7 depict alternative constructions of PLEDs utilizing aconcave-shaped multilayer optical film LP reflector. Spacing the LPreflector away from the phosphor and curving it in towards the phosphorand towards the LED 12 helps reduce the range of incidence angles ofexcitation light impinging on the LP reflector, thereby reducing theleakage of UV light through the LP reflector caused by the blue-shifteffect discussed above. Preferably the multilayer optical film ispermanently deformed by embossing or other suitable process into aconcave surface of suitable shape before immersion in transparent medium18. The multilayer optical films, whether LP or SP, are specularreflectors within their respective reflection bands. Diffuse reflectionfrom a multilayer optical film is typically negligible.

[0042] In FIG. 5, PLED 40 includes a relatively small area phosphorlayer 42 disposed on an optional SP reflector 44 composed of a polymericmultilayer optical film. LP reflector 46 has been embossed to acquire aconcave shape and positioned next to the other components (42, 44) ofthe phosphor-reflector assembly. LED 12 and heat sink 14 are arranged todirect UV excitation light emitted by the LED toward the central portionof phosphor layer 42. Preferably, the UV light has its highest fluenceat or near the center of phosphor layer 42. UV light not absorbed in itsinitial traversal of phosphor layer 42 passes through a region 48between LP reflector 46 and phosphor layer 42 before being reflected byLP reflector 46 back towards the phosphor layer. The region 48 can becomposed of transparent potting material 18, or alternatively of anotherpolymeric material, or air (or other gas), or glass. LP reflector 46 ispreferably shaped to maximize the amount of UV excitation lightreflected back to the phosphor.

[0043]FIG. 6 shows a PLED 50 similar to PLED 40, except that the size ofthe phosphor layer 52, SP reflector 54, and LP reflector 56 areincreased. For a given distance from LED 12 to the phosphor layer, andthe same heat sink 14 geometry, the larger LP reflector 56 will yield ahigher concentration of light in the center of the phosphor layer. Thesmaller, central emitting area of the phosphor layer presents a smallerrange of incidence angles of phosphor-emitted light to the surface ofthe LP reflector, improving overall PLED efficiency. As before, region58 can be composed of potting material 18 or another polymeric material,or air (or other gas), or glass.

[0044] PLED 60, shown in FIG. 7, is similar to PLED 50, except the LPreflector 66 now forms an outer surface of the light source. Region 68can be filled with potting material 18 or other transparent medium.

[0045] The phosphor layers of FIGS. 5-7 can be continuous, or patternedto limit the phosphor to where it is most effective. Moreover, in theembodiments of FIGS. 1 and 5-7 and other embodiments where thephosphor-reflector assembly is disposed above and spaced apart from theLED, the PLED can be manufactured in two halves: one containing the LEDwith heat sink, and the other containing the phosphor layer andmultilayer reflector(s). The two halves can be made separately, and thenbe joined or otherwise secured together. This construction technique canhelp simplify manufacturing and increase overall yields.

[0046]FIG. 8 demonstrates a concept that can be applied beneficially tothe other embodiments herein: providing an air gap between the LED andthe phosphor layer, and/or providing an air gap proximate to one or moreelements of the phosphor-reflector assembly. Only some elements of aPLED are shown in the figure for simplicity of description. An air gap70 is shown between LED 12 and phosphor layer 72, adjacent multilayeroptical film SP reflector 74. The air gap has a minimal detrimentaleffect on UV light from the LED reaching the phosphor layer because ofthe relatively small angles involved. But the air gap enables totalinternal reflection (TIR) of light traveling at high incidence angles,such as light traveling in the SP reflector, the phosphor layer, and theLP reflector. In the embodiment of FIG. 8 the efficiency of the SPreflector is enhanced by allowing TIR at the lower surface of reflector74. Alternatively, SP reflector 74 can be eliminated and the air gap canbe formed directly under phosphor layer 72. An air gap can also beformed at the upper side of phosphor layer 72, or adjacent to the LPreflector at its upper or lower surface. One approach for providing theair gap involves the use of known microstructured films. Such films havea substantially flat surface opposed to a microstructured surface. Themicrostructured surface can be characterized by a single set of linearv-shaped grooves or prisms, multiple intersecting sets of v-shapedgrooves that define arrays of tiny pyramids, one or more sets of narrowridges, and so forth. When the microstructured surface of such a film isplaced against another flat film, air gaps are formed between theuppermost portions of the microstructured surface.

[0047] As phosphors convert light of one wavelength (the excitationwavelength) to other wavelengths (the emitted wavelengths), heat isproduced. The presence of an air gap near the phosphor may significantlyreduce heat transmission from the phosphor to surrounding materials. Thereduced heat transfer can be compensated for in other ways, such as byproviding a layer of glass or transparent ceramic near the phosphorlayer that can remove heat laterally.

[0048] Still another approach of improving the efficiency of PLEDs is toconfigure the LED, phosphor layer, and LP reflector such that at leastsome of the UV light from the LED is reflected by the LP reflectordirectly onto the top (viewing) surface of the phosphor layer, ratherthan directing all of the UV light onto the bottom surface of thephosphor layer. FIG. 9 shows such a PLED 80. The heat sink 14′ has beenmodified from above embodiments so that the LED 12 and the phosphorlayer 82 can be mounted generally co-planar. An SP reflector is shownunderneath the phosphor layer, but in many cases will not be required.This is because LP reflector 86, which has been embossed in the form ofa concave ellipsoid or similar shape, directs UV excitation lightdirectly from the LED onto the upper surface of phosphor layer 82, whichsurface faces the front of PLED 80. The LED and phosphor layer arepreferably disposed at the foci of the ellipsoid. The visible lightemitted by the phosphor layer is transmitted by LP reflector 86 andcollected by the rounded front end of the PLED body to form the desiredpattern or visible (preferably white) light.

[0049] Directing excitation light directly at the front surface of thephosphor layer has a number of benefits. The brightest portion of thephosphor layer—where the excitation light is the strongest—now isexposed at the front of the device rather than being obscured throughthe thickness of the phosphor layer. The phosphor layer can be madesubstantially thicker so that it absorbs substantially all of the UVexcitation light, without concern for the thickness/brightness tradeoffreferred to above. The phosphor can be mounted on a broadband metalmirror, including silver or enhanced aluminum.

[0050]FIG. 10 shows schematically another PLED embodiment where the LEDlight impinges on the front surface of the phosphor layer, but whereinsome of the LED light also impinges on the back surface. In thisembodiment, some light emitted by LED 12 impinges on the back surface ofphosphor layer 92, but some LED light also reflects off of theconcave-shaped LP reflector 96 to strike the front surface of phosphorlayer 92 without traversing through the phosphor. Visible light emittedby phosphor layer 92 then passes through the LP reflector 96 towards theviewer or object to be illuminated. The LED, phosphor layer, and LPreflector can all be immersed or attached to a transparent pottingmedium as shown in previous embodiments.

[0051]FIG. 11 shows schematically another PLED embodiment, whereincombinations of non-imaging concentrators are arranged to enhance theoperation of the multilayer optical films. Specifically, concentratorelements 100 a, 100 b, 100 c are provided as shown between the LED 12,SP reflector 104, phosphor layer 102, and LP reflector 106. Theconcentrator elements have the effect of reducing the angular spread oflight impinging on the multilayer reflectors, thus reducing theblue-shift of the reflection band discussed above in connection withFIGS. 5-7. The concentrator elements may be in the form of simpleconical sections with flat sidewalls, or the sidewalls can take on amore complex curved shape as is known to enhance collimation or focusingaction depending on the direction of travel of the light. In any eventthe sidewalls of the concentrator elements are reflective and the twoends (one small, one large) are not. In FIG. 11, LED 12 is disposed atthe small end of concentrator 100 a. Concentrator element 100 a collectsa wide angular range of light emitted by the LED, which range is reducedby the time such light has traveled to the large end of concentratorelement 100 a, where SP reflector 104 is mounted. The SP reflectortransmits the UV excitation light to concentrator element 100 b, whichconcentrates such light onto phosphor layer 102 (while increasing theangular spread of the light). Wide angular range visible light emitteddownwardly by phosphor layer 102 is converted by concentrator element100 b to a more narrow angular range at SP reflector 104, where it isreflected back up towards the phosphor layer 102. Meanwhile, UV lightthat leaks through phosphor layer 102 and visible light emitted upwardlyby phosphor layer 102 initially has a wide angular spread, but isconverted by concentrator element 100 c to a smaller angular spread sothat LP reflector 106 will better transmit the visible light emitted bythe phosphor and reflect the UV light back towards the phosphor layer.

[0052] To capture as much LED excitation light as possible, the smallend of concentrator element 100 a can have a cavity so as to capture atleast some light emitted by the sides of the LED, as shown in FIG. 12.

[0053] The embodiments disclosed herein are operative with a variety ofphosphor materials. The phosphor materials are typically inorganic incomposition, having excitation wavelengths in the 300-450 nanometerrange and emission wavelengths in the visible wavelength range. In thecase of phosphor materials having a narrow emission wavelength range, amixture of phosphor materials can be formulated to achieve the desiredcolor balance, as perceived by the viewer, for example a mixture ofred-, green- and blue-emitting phosphors. Phosphor materials havingbroader emission bands are useful for phosphor mixtures having highercolor rendition indices. Desirably, phosphors should have fast radiativedecay rates. A phosphor blend can comprise phosphor particles in the1-25 micron size range dispersed in a binder such as epoxy, adhesive, ora polymeric matrix, which can then be applied to a substrate, such as anLED or a film. Phosphors that convert light in the range of about 300 to470 nm to longer wavelengths are well known in the art. See, forexample, the line of phosphors offered by Phosphor Technology Ltd.,Essex, England. Phosphors include rare-earth doped garnets, silicates,and other ceramics. The term “phosphor” as used herein can also includeorganic fluorescent materials, including fluorescent dyes and pigments.Materials with high stability under 300-470 nm radiation are preferred,particularly inorganic phosphors.

[0054] Glossary of Certain Terms

[0055] LED: a diode that emits light, whether visible, ultraviolet, orinfrared, and whether coherent or incoherent. The term as used hereinincludes incoherent (and usually inexpensive) epoxy-encasedsemiconductor devices marketed as “LEDs”, whether of the conventional orsuper-radiant variety. The term as used herein also includessemiconductor laser diodes.

[0056] Visible Light: light that is perceptible to the unaided humaneye, generally in the wavelength range from about 400 to 700 nm.

[0057] Optical Repeat Unit (“ORU”): a stack of at least two individuallayers which repeats across the thickness of a multilayer optical film,though corresponding repeating layers need not have the same thickness.

[0058] Optical thickness: the physical thickness of a given body timesits refractive index. In general, this is a function of wavelength andpolarization.

[0059] Reflection band: a spectral region of relatively high reflectancebounded on either side by regions of relatively low reflectance.

[0060] Ultraviolet (UV): light whose wavelength is in the range fromabout 300 to about 400 nm.

[0061] White light: light that stimulates the red, green, and bluesensors in the human eye to yield an appearance that an ordinaryobserver would consider “white”. Such light may be biased to the red.(commonly referred to as warm white light) or to the blue (commonlyreferred to as cool white light). Such light can have a color renditionindex of up to 100.

[0062] Further Discussion

[0063] The interference reflector described herein includes reflectorsthat are formed of organic, inorganic or a combination of organic andinorganic materials. The interference reflector can be a multilayerinterference reflector. The interference reflector can be a flexibleinterference reflector. A flexible interference reflector can be formedfrom polymeric, non-polymeric materials, or polymeric and non-polymericmaterials. Exemplary films including a polymeric and non-polymericmaterial are disclosed in U.S. Pat. Nos. 6,010,751 and 6,172,810 and EP733,919A2, all incorporated by reference herein.

[0064] The interference reflector described herein can be formed fromflexible, plastic, or deformable materials and can itself be flexible,plastic or deformable. These interference reflectors can be deflectableor curved to a radius usable with conventional LEDs, i.e., from 0.5 to 5mm. These flexible interference reflectors can be deflected or curvedand still retain its pre-deflection optical properties.

[0065] Known self-assembled periodic structures, such as cholestericreflecting polarizers and certain block copolymers, are considered to bemultilayer interference reflectors for purposes of this application.Cholesteric mirrors can be made using a combination of left and righthanded chiral pitch elements.

[0066] In an illustrative embodiment, a long-pass filter that partiallytransmits all wavelengths of blue light can be used in combination witha thin yellow phosphor layer in order to direct some blue light from theLED back onto the phosphor layer after the first pass through thephosphor.

[0067] In addition to providing reflection of UV light, a function ofthe multilayer optical film can be to block transmission of UV light soas to prevent degradation of subsequent elements inside or outside theLED package, including prevention of human eye damage. In someembodiments, it may be advantageous to incorporate a UV absorber on theside of the UV reflector furthest away from the LED. This UV absorbercan be in, on, or adjacent to the multilayer optical film.

[0068] Although a variety of methods are known in the art for producinginterference filters, an all polymer construction can offer severalmanufacturing and cost benefits. If high temperature polymers with highoptical transmission and large index differentials are utilized in theof an interference filter, then an environmentally stable filter that isboth thin and very flexible can be manufactured to meet the opticalneeds of short-pass (SP) and (LP) filters. In particular, coextrudedmultilayer interference filters as taught in U.S. Pat. No. 6,531,230(Weber et al.) can provide precise wavelength selection as well as largearea, cost effective manufacturing. The use of polymer pairs having highindex differentials allows the construction of very thin, highlyreflective mirrors that are freestanding, i.e. have no substrate but arestill easily processed. Such interference structures will not crack orshatter or otherwise degrade either when thermoformed or when flexed toa radius of curvature as small as 1 mm.

[0069] An all polymeric filter can be thermoformed into various 3Dshapes such as e.g. hemispherical domes (as described below). However,care must be taken to control the thinning to the correct amount overthe entire surface of the dome to create the desired angularperformance. Filters having a simple two dimensional curvature areeasier to create than 3D, compound shaped filters. In particular, anythin and flexible filter can be bent into a 2D shaped such as e.g. apart of a cylinder, in this case an all polymeric filter is not needed.Multilayer inorganic filters on thin polymeric substrates can be shapedin this manner, as well as can inorganic multilayers on glass substratesthat are less than 200 microns in thickness. The latter may have to beheated to temperatures near the glass transition point to obtain apermanent shape with low stress.

[0070] Optimum bandedges for long and short pass filters will depend onthe emission spectra of both the LED and the phosphor in the system thefilters are designed to operate in. In an illustrative embodiment, for ashort pass filter, substantially all of the LED emission passes throughthe filter to excite the phosphor, and substantially all of the phosphoremissions are reflected by the filter so they do not enter the LED orits base structure where they could be absorbed. For this reason, theshort pass defining bandedge is placed in a region between the averageemission wavelength of the LED and the average emission wavelength ofthe phosphor. In an illustrative embodiment, the filter is placedbetween the LED and the phosphor. If however, the filter is planar, theemissions from a typical LED will strike the filter at a variety ofangles, and at some angle of incidence be reflected by the filter andfail to reach the phosphor. Unless the filter is curved to maintain anearly constant angle of incidence, one may desire to place the designbandedge at a wavelength larger than the midpoint of the phosphor andLED emission curves to optimize the overall system performance. Inparticular, very little of the phosphor emission is directed to thefilter near zero degrees angle of incidence because the included solidangle is very small.

[0071] In another illustrative embodiment, long pass reflective filtersare placed opposite the phosphor layer from the LED in order to recyclethe LED excitation light back to the phosphor in order to improve systemefficiency. In the illustrative embodiment, a long pass filter may beomitted if the LED emissions are in the visible spectrum and largeamounts are needed to balance the phosphor color output. However, a longpass filter that partially transmits the shortwave light, such as e.g.blue light, can be used to optimize the angular performance of ablue-LED/yellow-phosphor system via the spectral angle shift that wouldpass more blue light at higher angles than at normal incidence.

[0072] In a further illustrative embodiment, the LP filter is curved, inorder to maintain a nearly constant angle of incidence of the LEDemitted light on the filter. In this embodiment, the phosphor and theLED both face one side of the LP filter. At high angles of incidence,the LP filter will not reflect the shortwave light. For this reason, thelong wave bandedge of the LP filter can be placed at as long awavelength as possible while blocking as little of the phosphor emissionas possible. Again, the bandedge placement can be changed to optimizethe overall system efficiency.

[0073] The term “adjacent” is defined herein to denote a relativepositioning of two articles that are near one another. Adjacent itemscan be touching, or spaced away from each other with one or morematerials disposed between the adjacent items.

[0074] LED excitation light can be any light that an LED source canemit. LED excitation light can be UV, or blue light. Blue light alsoincludes violet and indigo light. LEDs include spontaneous emissiondevices as well as devices using stimulated or super radiant emissionincluding laser diodes and vertical cavity surface emitting laserdiodes.

[0075] Layers of phosphor described herein can be a continuous ordiscontinuous layer. The layers of phosphor material can be a uniform ornon-uniform pattern. The layer of phosphor material can be plurality ofregions having a small area such as, for example, a plurality of “dots”each having an area in plan view of less than 10000 micrometers² or from500 to 10000 micrometers². In an illustrative embodiment, the pluralityof dots can each be formed from a phosphor which emits visible light atone or more different wavelengths such as, for example, a dot emittingred, a dot emitting blue, and a dot emitting green. The dots emittingvisible light at a plurality of wavelengths can be arranged andconfigured in any uniform or non-uniform manner as desired. For example,the layer of phosphor material can be a plurality of dots with anon-uniform density gradient along a surface or an area. The “dots” canhave any regular or irregular shape, and need not be round in plan view.Phosphor material can be in a co-extruded skin layer of the multilayeroptical film.

[0076] Structured phosphor layers can be configured in several ways toprovide benefits in performance, as described below. When multiplephosphor types are used to provide broader or fuller spectral output,light from shorter wavelength phosphors can be re-absorbed by otherphosphors. Patterns comprising isolated dots, lines, or isolated regionsof each phosphor type reduce the amount of re-absorption. This would beparticularly effective in cavity type constructions where unabsorbedpump light is reflected back to the phosphor pattern.

[0077] Multilayer structures can also reduce absorption. For example, itcould be advantageous to form layers of each phosphor in sequence, withthe longest wavelength emitter nearest the excitation source. Lightemitted nearer the emitter will on average, undergo multiple scatteringwithin the total phosphor layer to a greater extent than light emittednear the output surface. Since the shortest wavelength emitted is mostprone to re-absorption, it is advantageous to locate the shortestwavelength phosphor nearest to the output surface. In addition, it maybe advantageous to use different thicknesses for each layer, so as tocompensate for the progressively lower intensity of the excitation lightas it propagates through the multilayer structure. For phosphor layerswith similar absorption and emission efficiency, progressively thinnerlayers from excitation to output side would provide compensation for thedecreasing excitation intensity in each layer. It would also beadvantageous to place short pass filters in-between the differentphosphor layers so as to reduce emitted phosphor light from scatteringbackward and being re-absorbed by phosphor layers earlier in thesequence.

[0078] Forming film structures with phosphor coating also enablesmanufacturing of arrays of small structures suitable for dicing intoindividual units for diodes. For example, an array of small domes orhemispheres could be printed, each of which would be useful for reducingthe “halo effect” sometimes present for PLED's (as described below).

[0079] Non-scattering phosphor layers can provide enhanced light outputin combination with multilayer optical films. Non-scattering phosphorlayers can comprise conventional phosphors in an index-matched binder(for example, a binder with high index inert nanoparticles), nanosizeparticles of conventional phosphor compositions (for examples, whereparticle sizes are small and negligibly scatter light), or through theuse of quantum dot phosphors. Quantum dot phosphors are light emittersbased on semiconductors such as cadmium sulfide, wherein the particlesare sufficiently small so that the electronic structure is influencedand controlled by the particle size. Hence, the absorption and emissionspectra are controlled via the particle size. Quantum dots are disclosedin U.S. Pat. No. 6,501,091, incorporated by reference herein.

[0080] Embodiments are disclosed herein where a first optical componentcomprising a phosphor/reflector assembly can be later attached to an LEDbase; a heat sink can optionally include a transparent heat sink towhich the phosphor layer and interference filter may be attached. Thetransparent heat sink can be a layer of sapphire disposed between thephosphor layer/interference filter and the LED base. Most glasses have ahigher thermal conductivity than polymers and can be useful in thisfunction as well. Many other crystalline material's thermalconductivities are higher than most glasses and can be used here also.The sapphire layer can be contacted at the edges by a metal heat sink.

[0081] In an illustrative embodiment, prior to coating the interferencefilter (i.e., polymeric interference filter with a phosphor layer, thesurface of the filter can be treated to promote adhesion of the coating.The optimum treatment depends both on the surface layer of the filterand on the materials in the phosphor coating, specifically the binderused to hold the phosphor particles on the surface. The surfacetreatment can be a standard corona discharge treatment, or a coronadischarge followed by a priming layer. The priming layer is typicallyless than 1 micron thick. Useful priming materials are PVDC, sulphonatedpolyesters and other amorphous polyesters such as Vitel, maleatedcopolymers such as Bynel (Dupont) and Admer (Mitsui Chemicals), and EVAsuch as Elvax (Dupont). Binders for the phosphor layer can be athermoplastic and/or thermoformable and can be a fluoropolymer, orsilicon based material, for example.

[0082] Alternative priming layers include, for example, vacuum coatedlayers, preferably from energetic sources such as ion-beam or gas plasmasources wherein the ions or plasma components bombard the polymersurface while depositing the priming layer. Such priming layers aretypically inorganic material layers such as titania or silica layers.

[0083] Although much attention has been given to the use of phosphorsfor down-converting short wavelength light to visible light, it is alsopossible to up-convert infrared radiation to visible light.Up-converting phosphors are well known in the art and typically use twoor more infrared photons to generate 1 visible photon. Infrared LEDsneeded to pump such phosphors have also been demonstrated and are veryefficient. Visible light sources that use this process can be made moreefficient with the addition of long-pass (LP) and short-pass (SP)filters although the functions of each are reversed in this casecompared to the down-converting phosphor systems. A SP filter can beused to direct IR light towards the phosphor while transmitting thevisible light, and an LP filter can be placed between the phosphor andLED to direct the emitted visible light outward towards the intendedsystem or user.

[0084] The lifetime of an SP or LP filter is preferably greater than orequal to the lifetime of the LED in the same system. The degradation ofa polymeric interference filter can be due to overheating which cancause material creep which changes the layer thickness values andtherefore the wavelengths that the filter reflects. In the worst case,overheating can cause the polymer materials to melt, resulting in rapidflow of material and change in wavelength selection as well as inducingnon-uniformities in the filter.

[0085] Degradation of polymer materials can also be induced by shortwavelength (actinic) radiation such as blue, violet or UV radiation,depending on the polymer material. The rate of degradation is dependentboth on the actinic light flux and on the temperature of the polymer.Both the temperature and the flux will in general, decrease withincreasing distance from the LED. Thus it is advantageous in cases ofhigh brightness LEDs, particularly UV LEDs, to place a polymeric filteras far from the LED as the design can allow. Placement of the polymerfilter on a transparent heat sink as descibed above can also improve thelifetime of the filter. For domed filters, the flux of actinic radiationdecreases as the square of the distance from the LED. For example, ahemispherical MOF reflector with a 1 cm radius, placed with aunidirectional 1 watt LED at the center of curvature, would experiencean average intensity of 1/(2π) Watts/cm² (surface area of the dome=2πcm²). At a 0.5 cm radius, the average intensity on the dome would befour times of that value, or 2/π W/cm². The system of LED, phosphor, andmultilayer optical film can be designed with light flux and temperaturecontrol taken into consideration.

[0086] A reflective polarizer can be disposed adjacent the multilayerreflector and/or adjacent the phosphor material. The reflectivepolarizer allows light of a preferred polarization to be emitted, whilereflecting the other polarization. The phosphor layer and other filmcomponents known in the art can depolarize the polarized light reflectedby reflective polarizer, and either by the reflection of the phosphorlayer, or phosphor layer in combination with the multilayer reflector,light can be recycled and increase the polarized light brightness of thesolid state light device (LED). Suitable reflective polarizers include,for example, cholesteric reflective polarizers, cholesteric reflectivepolarizers with a ¼ wave retarder, DBEF reflective polarizer availablefrom 3M Company or DRPF reflective polarizer also available from 3MCompany. The reflective polarizer preferably polarizes light over asubstantial range of wavelengths and angles emitted by the phosphor, andin the case where the LED emits blue light, may reflect the LED emissionwavelength range as well.

[0087] Suitable multilayer reflector films are birefringent multilayeroptical films in which the refractive indices in the thickness directionof two adjacent layers are substantially matched and have a Brewsterangle (the angle at which reflectance of p-polarized light goes to zero)which is very large or is nonexistant. This allows for the constructionof multilayer mirrors and polarizers whose reflectivity for p-polarizedlight decreases slowly with angle of incidence, are independent of angleof incidence, or increase with angle of incidence away from the normal.As a result, multilayer films having high reflectivity (for both planesof polarization for any incident direction in the case of mirrors, andfor the selected direction in the case of polarizers) over a widebandwidth, can be achieved. These polymeric multilayer reflectorsinclude alternating layers of a first and second thermoplastic polymer.The alternating layers defining a local coordinate system with mutuallyorthogonal x- and y-axes extending parallel to the layers and with az-axis orthogonal to the x- and y-axes, and wherein at least some of thelayers are birefringent. The absolute value of the difference in indicesof refraction between the first and second layers is Δx, Δy, and Δzrespectively, for light polarized along first, second, and thirdmutually orthogonal axes. The third axis is orthogonal to the plane ofthe film where Δx is greater than about 0.05, and where Δz is less thanabout 0.05. These films are described, for example, in U.S. Pat. No.5,882,774, which is incorporated by reference herein.

[0088] Non-planar is defined as surface that is not flat. A non-planarsurface can be formed, for example, by deflecting a flat article forminga curved article. The non-planar multilayer reflectors can be castdirectly into a non-planar shaped article or thermoformed from a planarmultilayer reflector into a non-planar multilayer reflector. Thenon-planar multilayer reflectors can be a concave shape. In anillustrative embodiment, the non-planar multilayer reflector can be ahemispherical concave shape. The LED can be located at or near thecenter of curvature of the non-planar multilayer reflector. In anillustrative embodiment, the non-planar multilayer reflector is ahemispherical concave shape opening towards the LED. The lateral extentof the light emitting region of the LED can be less than ⅓, or less than⅙ of the minimum radius of curvature of the non-planar multilayerreflector.

[0089]FIG. 13 is a schematic sectional view of another embodiment of aPLED construction 210. A non-planar multilayer reflector 224 is shownadjacent a layer of phosphor material 222, however the non-planarmultilayer reflector 224 need only be positioned such that light cantravel between the layer of phosphor material 222 and the multilayerreflector 224. The non-planar multilayer reflector 224 reflects LEDexcitation light excitation light such as, for example UV, or blue lightand transmits visible light. This non-planar multilayer reflector 224can be referred to as a long-pass (LP) reflector, as described above.The above arrangement can be disposed within an optically transparentmaterial 220.

[0090] The non-planar multilayer reflector 224 can be positioned toreceive light from an LED 212, as discussed herein. The non-planarmultilayer reflector 224 can be any useable thickness. The non-planarpolymeric multilayer reflector 224 can be 5 to 200 micrometers thick or10 to 100 micrometers thick. The non-planar multilayer reflector 224 canoptionally be substantially free of inorganic materials.

[0091] The non-planar multilayer reflector 224 can be formed of amaterial that resists degradation when exposed to V, blue or violetlight such, as discussed herein. The multilayer reflectors discussedherein can be stable under high intensity illumination for extendedperiods of time. High intensity illumination can be generally defined asa flux level from 1 to 100 Watt/cm². Operating temperatures at theinterference reflectors can be 100° C. or less, or 65° or less. Suitableillustrative polymeric materials can include UV resistant materialformed from, for example, acrylic material, PET material, PMMA material,polystyrene material, polycarbonate material, THV material availablefrom 3M (St. Paul, Minn.), and combinations thereof. These materials andPEN material can be used for blue excitation light.

[0092] The non-planar multilayer reflector 224 can have a non-uniformthickness or thickness gradient along its length, width, or both. Thenon-planar multilayer reflector 224 can have a first thickness at aninner region 223 of the non-planar multilayer reflector 224 and a secondthickness at an outer region 225 of the non-planar multilayer reflector224. The difference in thickness across the surface of the reflector isassociated with a corresponding difference or shift in spectralreflectance, with the thinner areas being blue-shifted relative to thethicker areas. There are a variety of ways that thickness gradients canbe created. For example, thickness gradients can be formed bythermoforming, embossing, laser embossing, or extrusion, to list a few.

[0093] As shown in FIG. 13, the inner region 223 thickness can begreater than the outer region 225 thickness. Increasing the inner region223 thickness can reduce an undesirable effect know as the “haloeffect”. The “halo effect” is a problem known in industry where thebalance of blue excitation light and yellow converted light changes as afunction of viewing angle of the LED. Here, the inner region 223thickness can be greater than the outer region 225 thickness so as toreduce on-axis blue transmission.

[0094] As shown in FIG. 14, the outer region 325 thickness can begreater than the inner region 323 thickness. The above arrangement canbe disposed within an optically transparent material 320.

[0095] The non-planar multilayer reflector can be positioned in anyusable configuration with the LED, as described herein. In anillustrative embodiment, the non-planar multilayer reflector ispositioned between the layer of phosphor and the LED (see e.g., FIGS.15-17). In another illustrative embodiment, the layer of phosphor ispositioned between the non-planar multilayer reflector and the LED (seee.g., FIGS. 13, 14, 16-21).

[0096] The non-planar multilayer reflector 224/324 can be configured toreflect UV or blue light and transmit at least a portion of the visiblelight spectrum such as green, yellow, or red light. In anotherillustrative embodiment, the non-planar multilayer reflector 224/324 canbe configured to reflect UV, blue or green light and transmit at least aportion of the visible light spectrum such as yellow or red light.

[0097] The layer of phosphor material 222/322 is capable of emittingvisible light when illuminated with excitation light emitted from an LED212/312. The layer of phosphor material can be any useable thickness.The layer of phosphor material can include any number of binders suchas, for example, a polyester material. In another illustrativeembodiment the layer of phosphor material can include an adhesivematerial. The adhesive material can be an optically functional adhesive.

[0098]FIG. 15 is a schematic sectional view of another embodiment of aPLED construction 410. A non-planar multilayer reflector 426 is shownadjacent a layer of phosphor material 422, however the non-planarmultilayer reflector 426 need only be positioned such that light cantravel between the layer of phosphor material 422 and the non-planarmultilayer reflector 426. The non-planar multilayer reflector 426reflects visible light and transmits LED excitation light such as, forexample UV, or blue light. This non-planar multilayer reflector 426 canbe referred to as a short-pass (SP) reflector, as described above. Theabove arrangement can be disposed within an optically transparentmaterial 420.

[0099] The non-planar multilayer reflector 426 may include the samematerials and be formed in a similar manner as the non-planar multilayerreflector 424 described above. The phosphor layer 422 is also describedabove.

[0100] The non-planar multilayer reflector 426 can be positioned in anyusable configuration with the LED 412 as described herein. In anillustrative embodiment shown as FIG. 15, the non-planar multilayerreflector 426 is positioned between the layer of phosphor 422 and theLED 412. In another illustrative embodiment, the layer of phosphor 422is positioned between the non-planar multilayer reflector 426 and theLED 412. In an illustrative embodiment, non-planar multilayer reflector426 is a hemispherical concave shape facing toward the LED 412. Such adesign allows light emitted by the LED 412 to strike the non-planarmultilayer reflector 426 at a normal or a near normal incidence angle.The non-planar geometry of the multilayer reflector 426 allowssubstantially all short wave light to pass through the non-planarmultilayer reflector 426 no matter what side or direction it emanatesfrom the LED 412.

[0101]FIG. 16 is a schematic sectional view of another embodiment of aPLED construction 510. A first non-planar multilayer reflector 524 isshown spaced away from a layer of phosphor material 522, however thefirst non-planar multilayer reflector 524 need only be positioned suchthat light can travel between the layer of phosphor material 522 and thefirst non-planar multilayer reflector 524. The first non-planarmultilayer reflector 524 reflects LED excitation light excitation lightsuch as, for example UV, or blue light and transmits visible light. Thisfirst non-planar multilayer reflector 524 can be referred to as along-pass (LP) reflector, as described above. The above arrangement canbe disposed within an optically transparent material 520.

[0102] A second non-planar multilayer reflector 526 is shown adjacent alayer of phosphor material 22, however the second non-planar multilayerreflector 526 need only be positioned such that light can travel betweenthe layer of phosphor material 522 and the second non-planar multilayerreflector 526. The second non-planar multilayer reflector 526 reflectsvisible light and transmits LED excitation light such as, for exampleUV, or blue light. This second non-planar multilayer reflector 526 canbe referred to as a short-pass (SP) reflector, as described above.

[0103] A phosphor layer 522 is shown disposed between the firstnon-planar polymeric multilayer reflector 524 and the second non-planarpolymeric multilayer reflector 526. The phosphor layer 522 is describedabove.

[0104]FIG. 17 is a schematic sectional view of another embodiment of aPLED construction 610. A first non-planar multilayer reflector 624 isshown adjacent a layer of phosphor material 622, however the firstnon-planar multilayer reflector 624 need only be positioned such thatlight can travel between the layer of phosphor material 622 and thefirst non-planar multilayer reflector 624. The first non-planarmultilayer reflector 624 reflects LED excitation light excitation lightsuch as, for example UV, or blue light and transmits visible light. Thisfirst non-planar multilayer reflector 624 can be referred to as along-pass (LP) reflector, as described above. The above arrangement canbe disposed within an optically transparent material 620.

[0105] A second non-planar multilayer reflector 626 is shown adjacent alayer of phosphor material 622, however the second non-planar multilayerreflector 626 need only be positioned such that light can travel betweenthe layer of phosphor material 622 and the second non-planar multilayerreflector 626. The second non-planar multilayer reflector 626 reflectsvisible light and transmits LED excitation light such as, for exampleUV, or blue light. This second non-planar multilayer reflector 626 canbe referred to as a short-pass (SP) reflector, as described above.

[0106] A phosphor layer 622 is shown disposed between the firstnon-planar multilayer reflector 624 and the second non-planar multilayerreflector 626. The phosphor layer 622 is described above.

[0107]FIG. 18 is a sectional view of another embodiment of a PLEDconstruction 710. A non-planar multilayer reflector 724 is shown spacedaway from a layer of phosphor material 722, however the non-planarmultilayer reflector 724 need only be positioned such that light cantravel between the layer of phosphor material 722 and the non-planarmultilayer reflector 724. The non-planar multilayer reflector 724reflects LED excitation light excitation light such as, for example UV,or blue light and transmits visible light. This non-planar multilayerreflector 724 can be referred to as a long-pass (LP) reflector, asdescribed above.

[0108] A phosphor layer 722 is shown disposed between the LED 712 andthe non-planar polymeric multilayer reflector 724. The phosphor layer722 is also described above. The phosphor layer 722 is shown in FIG. 18as a dome of phosphor material encompassing the LED 712.

[0109] The non-planar multilayer reflector 724 and phosphor layer 722 isshown disposed within an optically transparent body 718. The non-planarmultilayer reflector 724 can be located at any position within or on asurface 720 of the optically transparent body 718.

[0110] The phosphor layer 722 can be located at any position within oron a surface 720 of the optically transparent body 718. For example, thephosphor layer 722 can be disposed adjacent the LED 712 as shown in FIG.18. In another illustrative embodiment, the phosphor layer 822 can bespaced apart from the LED 812 as shown in FIG. 19. In anotherillustrative embodiment, the phosphor layer 922 can be disposed withinor on the entire optically transparent body 918 as shown in FIG. 20. Inanother illustrative embodiment, the phosphor layer 1022 can be disposedon or in the optically transparent body 1018 such that the phosphorlayer 1022 has a greater thickness or density at normal angles ofincident from the LED 1012 and decreasing in thickness or density as theangles of incident from the LED 1012 become greater. Thus, the phosphorlayer 1022 can have a volume density gradient, and/or a surface areadensity gradient as a function of LED 1012 incident angle as shown inFIG. 21.

EXAMPLES

[0111] Measurement of phosphor luminescence herein was made using aspectroradiometer (designated OL 770-LED by Optronic Laboratories, Inc.,Orlando, Fla. USA) fitted with an integrating sphere (designated OLIS-670-LED by Optronic Laboratories) and a high precision LED holder(designated OL 700-80-20 by Optronic Laboratories). Thespectroradiometer is calibrated to report the total radiant energyentering the integrating sphere at the input port (in units of Watts pernanometer). A 1 inch diameter disk was made from the phosphor coatedsample using a custom punch. This disk fits into a custom film adaptormade to mount on the high precision LED holder. The custom adaptor holdsthe film sample approximately one inch above the base of the packagedLED. Measurements were performed by mounting an LED into the holder,placing the film with the phosphor coating into the adaptor, affixingthe adaptor to the light-emitting diode mount and then inserting thediode mount assembly into the entrance aperture of the integratingsphere. If necessary, calibrated neutral density filters were used toadjust the light level reaching the detector of the spectroradiometer.

[0112] Unless otherwise stated, the multilayer optical films used in thefollowing examples reflected both polarization states equally at normalincidence (i.e., each of the individual optical layers had nominallyequal refractive indices along orthogonal in-plane axes).

[0113] For all of the following examples in which the thickness of thephosphor layer is given, the thickness was determined by subtracting thethickness of the substrate film from the thickness of the phosphor layerand substrate film together. The thicknesses were measured using a dialindicator (catalog number 52-520-140 by Fred V. Fowler Co., Inc., ofNewton, Mass. USA) with a flat contact point (catalog number 52-525-035,also from Fowler) mounted on a dial gage stand (catalog number52-580-020, also from Fowler). The thickness of the substrate film wasthe average of three measurements at random locations on the substratefilm. The thickness of the phosphor layer and substrate film was theaverage of six measurements taken at random locations on the phosphorlayer.

Example 1

[0114] A coating of cerium-doped yttrium aluminum garnet (YAG:Ce)phosphor was made on single layer clear poly(ethylene terephthalate)(PET) film by the following procedure.

[0115] 12.00 grams of fluorpolymer resin (designated “Phosphor Ink PartA: Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035by Durel Company of Chandler, Ariz. USA) was placed into a 40 milliliterglass jar. 15.02 grams of YAG:Ce phosphor (designated QMK58/F-U1 Lot#13235 by Phosphor Technology, Ltd. of Stevenage, England) was measuredinto a weighing dish. The phosphor was mixed into the resin by firstadding one-half of the phosphor to the resin and mixing it in by handwith a stainless steel spatula and then adding the other half and mixingit by hand. The phosphor and resin were mixed by hand until the mixturehad a smooth texture and uniform appearance. The jar containing theresulting phosphor paste was covered with a lid and placed on a bottleroller for about 30 minutes.

[0116] A sheet of single layer clear PET film 3M Company (St. Paul,Minn.) 6 inches wide by 10 inches long by 1.5 mils thick was placed on aclean flat surface. Both surfaces of the PET film were wiped with alint-free cotton cloth dampened with methanol. The jar containing thephosphor paste was removed from the bottle roller and about 5 grams ofpaste was placed into a small puddle on the PET film. The phosphor pastewas hand-drawn into a coating using the 5 mil gap of a square multipleclearance applicator (designated PAR-5357 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA). Aftercuring, the phosphor/resin coating thickness was 1.6 mils.

[0117] A 1 inch diameter disk of the YAG:Ce coated film was prepared andmounted into the spectroradiometer as described above. The disk wasoriented with the phosphor coated side facing into the integratingsphere. A blue LED (designated Part #25-365 by Hosfelt Electronics,Inc., Steubenville, Ohio) with a peak wavelength of about 463 nm wasused to excite the phosphor. The standard 5 mm package for the blue LEDwas modified by machining off the domed lens at the top of the packageto provide a flat exit face for the blue light. Approximately 0.18 inchof the package was removed from the top of the package. The LED waspowered at 20 milliamps and 3.46 volts by a constant current powersupply. The emission spectra of the phosphor layer recorded using thespectroradiometer is shown in FIG. 22 as the curve labeled “Example 1”.Using software supplied with the spectroradiometer, the total luminousflux emitted into the integrating sphere was calculated to be 0.068lumens.

Example 2

[0118] A piece of multi-layer optical film (MOF) having alternatinglayers of PET and co-PMMA and having a normal-incidence reflection band(measured at half-maximum) from about 600 nm to about 1070 nm (made inaccordance with U.S. Pat. No. 6,531,230) was placed in the film adaptorbetween the phosphor coated PET film of Example 1 and the blue LED ofExample 1 (operated at 20 milliamps). The spectrum was recorded and isshown in FIG. 22 as the curve labeled “Example 2”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.118 lumens. Thisrepresents an increase in luminous intensity of 73%.

Example 3

[0119] A coating of zinc sulfide (ZnS) phosphor was made on poly(ethylene terepthalate) (PET) film by the following procedure:

[0120] 20.04 grams of fluorpolymer resin (designated “Phosphor Ink PartA: Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035by Durel Company of Chandler, Ariz., USA) was placed into a 2 ounceglass jar. 20.06 grams of ZnS phosphor (designated GL29A/N-C1 Lot #11382by Phosphor Technology, Ltd. of Stevenage, England) was measured into aweighing dish. The phosphor was mixed into the resin by first addingone-half of the phosphor to the resin and mixing it in by hand with astainless steel spatula and then adding the other half and mixing it byhand. The phosphor and resin were mixed by hand until the mixture had asmooth texture and uniform appearance. The jar containing the resultingphosphor paste was covered with a lid and placed on a bottle roller forabout 24 hours.

[0121] A sheet of clear PET film by 3M Company (St. Paul, Minn.) 6inches wide by 10 inches long by 1.5 mils thick was placed on a clearflat surface. Both surfaces of the PET film were wiped with a lint-freecotton cloth dampened with methanol. The jar containing the phosphorpaste was removed from the bottle roller and about 3 grams of paste wasplaced onto the PET film. The phosphor paste was hand-drawn into acoating using the 2 mil gap of a square multiple clearance applicator(designated PAR-5353 by BYK-Gardner USA of Columbia, Md., USA). The wetfilm was cured at a temperature of about 130° C. for 30 minutes in agravity convection oven (designated Model 1350G by VWR International,Inc., of West Chester, Pa., USA). After curing the phosphor/resincoating thickness was 0.7 mils.

[0122] A one inch diameter disk of the ZnS coated film was prepared andmounted into the spectroradiometer as described above. The disk wasoriented with the phosphor coated side facing into the integratingsphere. A UV LED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor fluorescence. The standard 5 mm package for the UVLED was modified by machining off the domed top of the package toprovide a flat exit face for the UV light. Approximately 0.180 inches ofthe package was removed from the top of the package. The LED was poweredat 20 milliamps and 3.7 volts by a constant current power supply. Theemission spectra of the phosphor layer recorded using thespectroradiometer is shown in FIG. 23 as the curve labeled “Example 3”.Using software supplied with the spectroradiometer, the total luminousflux emitted into the integrating sphere was calculated to be 0.052lumens.

Example 4

[0123] A piece of multi-layer optical film (MOF) having alternatinglayers of PET and co-PMMA and having a normal-incidence reflection band(measured at half-maximum) from about 320 nm to about 490 nm (made inaccordance with U.S. Pat. No. 6,531,230) was placed in the film adaptoron top of the phosphor layer of Example 3, and the UV LED of Example 3(operated at 20 milliamps) was used as the excitation source. Thespectrum was recorded and is shown in FIG. 23 as the curve labeled“Example 4”. Using software supplied with the spectroradiometer, thetotal luminous flux emitted into the integrating sphere was calculatedto be 0.062 lumens. This represents an increase in luminous intensitywhen compared to Example 3 of about 19%.

Example 5

[0124] A broadband visible reflector was made by laminating two piecesof multi-layer optical film (MOF). A layer of MOF having alternatinglayers of PET and co-PMMA and a normal-incidence reflection band(measured at half-maximum) from about 490 nm to about 610 nm(manufactured by 3M Company of St. Paul, Minn.) was laminated to a layerof MOF having alternating layers of PET and co-PMMA and having anormal-incidence reflection band (measured at half-maximum) from about590 nm to about 710 nm (manufactured by 3M Company of St. Paul, Minn.)using a optically clear adhesive. The laminate was placed in the filmadaptor between the phosphor coated PET film of Example 3, and the UVLED of Example 3 (operated at 20 milliamps). A piece of multi-layeroptical film (MOF) having alternating layers of PET and co-PMMA andhaving a normal-incidence reflection band (measured at half-maximum)from about 320 nm to about 490 nm (manufactured by 3M Company of St.Paul, Minn.) was placed in the film adaptor on top of the phosphor layerto create a cavity having a phosphor layer sandwiched between a visiblemirror on the LED side and a UV/blue mirror on the other side. Thespectrum was recorded and is shown in FIG. 23 as the curve labeled“Example 5”. Using software supplied with the spectroradiometer, thetotal luminous flux emitted into the integrating sphere was calculatedto be 0.106 lumens. This represents an increase in luminous intensitywhen compared to Example 3 of about 104%.

Example 6

[0125] A coating of zinc sulfide (ZnS) phosphor was made on poly(ethylene terepthalate) (PET) film by the following procedure:

[0126] The phosphor paste described in Example 3 was coated onto a sheetof clear PET film 6 inches wide by 10 inches long by 1.5 mils thick. ThePET was placed on top of a clean flat surface. Both surfaces of the PETfilm were wiped with a lint-free cotton cloth dampened with methanol.About 3 grams of paste was placed onto the PET film. The phosphor pastewas hand-drawn into a coating using the 4 mil gap of a square multipleclearance applicator (designated PAR-5353 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA). Aftercuring, the phosphor/resin coating thickness was 1.3 mils.

[0127] A one inch diameter disk of the ZnS coated film was prepared andmounted into the spectroradiometer as described above. The disk wasoriented with the phosphor coated side facing into the integratingsphere. A UV LED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor. The standard 5 mm package for the UV LED wasmodified by machining off the domed top of the package to provide a flatexit face for the UV light. Approximately 0.180 inches of the packagewas removed from the top of the package. The LED was powered at 20milliamps and 3.7 volts by a constant current power supply. The emissionspectra of the phosphor layer recorded using the spectroradiometer isshown in FIG. 24 as the curve labeled “Example 6”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.066 lumens.

Example 7

[0128] A piece of multi-layer optical film (MOF) having alternatinglayers of PET and co-PMMA and having a normal-incidence reflection band(measured at half-maximum) from about 490 nm to about 610 nm(manufactured by 3M Company of St. Paul, Minn.) was placed in the filmadaptor between the phosphor coated PET film of Example 6 and the UV LEDof Example 6 (operated at 20 milliamps). The spectrum was recorded andis shown in FIG. 24 as the curve labeled “Example 7”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.095 lumens. Thisrepresents an increase in luminous intensity when compared to Example 6of about 44%.

Example 8

[0129] A coating of zinc sulfide (ZnS) phosphor was made on multi-layeroptical film (MOF) by the following procedure:

[0130] The phosphor paste described in Example 3 was coated onto a sheetof MOF having alternating layers of PET and co-PMMA and having anormal-incidence reflection band (measured at half-maximum) from about490 nm to about 610 nm (manufactured by 3M Company of St. Paul, Minn.).The MOF was placed on top of a clean flat surface. Both surfaces of theMOF film were wiped with a lint-free cotton cloth dampened withmethanol. About 3 grams of paste was placed onto the MOF film. Thephosphor paste was hand-drawn into a coating using the 4 mil gap of asquare multiple clearance applicator (designated PAR-5353 by BYK-GardnerUSA of Columbia, Md., USA). The wet film was cured at a temperature ofabout 130° C. for 30 minutes in a gravity convection oven (designatedModel 1350G by VWR International, Inc., of West Chester, Pa., USA).After curing, the phosphor/resin coating thickness was 1.3 mils.

[0131] A one inch diameter disk of the ZnS coated film was prepared andmounted into the spectroradiometer as described above. The disk wasoriented with the phosphor coated side facing into the integratingsphere. A UV LED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor. The standard 5 mm package for the UV LED wasmodified by machining off the domed top of the package to provide a flatexit face for the UV light. Approximately 0.180 inches of the packagewas removed from the top of the package. The LED was powered at 20milliamps and 3.7 volts by a constant current power supply. The emissionspectra of the phosphor layer recorded using the spectroradiometer isshown in FIG. 24 as the curve labeled “Example 8”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.107 lumens. Thisrepresents an increase in luminous intensity when compared to Example 6of about 62%.

Example 9

[0132] A coating of zinc sulfide (ZnS) phosphor was screen printed onthe laminated multi-layer optical film (MOF) described in Example 5 bythe following procedure:

[0133] 150 grams of fluorpolymer resin (designated “Phosphor Ink Part A:Resin Solution”, part number: 1IN001, rev: AA, batch number: KY4-035 byDurel Company of Chandler, Ariz., USA) was placed into a 16 ounce glassjar. 150 grams of ZnS phosphor (designated GL29A/N-C1 Lot #11382 byPhosphor Technology, Ltd. of Stevenage, England) was measured into aweighing dish. The phosphor was slowly mixed into the resin using aglass impeller driven by an air motor. The phosphor and resin were mixeduntil the mixture had a smooth texture and uniform appearance. The jarcontaining the resulting phosphor paste was covered with a lid andplaced on a bottle roller for about 10 minutes.

[0134] The printing was done using a halftone pattern with a resolutionof 28 lines per inch on a 280 thread per inch PET screen mounted on ascreen printer (designated Type SSM by Svecia Silkscreen Maskiner AB, ofStockholm, Sweden). The halftone pattern consisted of three regionshaving 10%, 50% and 90% coverage. The pattern was printed in one passonto a sheet of the two laminated MOF films described in Example 5.

[0135] The printed layer was cured at a temperature of about 138° C. for15 minutes in a forced air oven. After curing, the phosphor/resincoating thickness was 0.8 mils.

[0136] A one inch diameter disk of the ZnS screen printed film from theportion of the pattern having 50% coverage was prepared and mounted intothe spectroradiometer as described above. The disk was oriented with thephosphor coated side facing into the integrating sphere. A UV LED(designated Part #25-495 by Hosfelt Electronics, Inc of Steubenville,Ohio) with a peak wavelength of about 395 nm was used to excite thephosphor. The standard 5 mm package for the UV LED was modified bymachining off the domed top of the package to provide a flat exit facefor the UV light. Approximately 0.180 inches of the package was removedfrom the top of the package. The LED was powered at 20 milliamps and 3.7volts by a constant current power supply. The emission spectra of thephosphor layer recorded using the spectroradiometer is shown in FIG. 25as the curve labeled “Example 9”. Using software supplied with thespectroradiometer, the total luminous flux emitted into the integratingsphere was calculated to be 0.052 lumens.

Example 10

[0137] A piece of multi-layer optical film (MOF) having alternatinglayers of PET and co-PMMA and having a normal-incidence reflection band(measured at half-maximum) from about 320 nm to about 490 nm(manufactured by 3M Company of St. Paul, Minn.) was placed in the filmadaptor on top of the phosphor layer of Example 9, and the UV LED ofExample 9 (operated at 20 milliamps) was used as the excitation source.The spectrum was recorded and is shown in FIG. 25 as the curve labeled“Example 10”. Using software supplied with the spectroradiometer, thetotal luminous flux emitted into the integrating sphere was calculatedto be 0.078 lumens. This represents an increase in luminous intensitywhen compared to Example 9 of about 50%.

Example 11

[0138] A thermoformed dome of multilayer optical film (MOF) coated withzinc sulfide (ZnS) phosphor was made by the following procedure.

[0139] A layer of MOF having alternating layers of PET and co-PMMA andhaving a normal-incidence reflection band (measured at half-maximum)from about 590 nm to about 710 nm (manufactured by 3M Company of St.Paul, Minn., USA) was bonded to a sheet of poly (vinyl chloride) to forma flexible composite. This composite will be referred to as MOF-PVC.

[0140] The MOF-PVC was placed on a clean flat surface with the MOF sidefacing up. The top surface of the MOF-PVC was wiped with a lint freecotton cloth dampened with methanol. About 3 grams of the ZnS phosphorpaste described in Example 9 was placed onto the MOF-PVC. The phosphorpaste was hand-drawn into a coating using the 4 mil gap of a squaremultiple clearance applicator (designated PAR-5353 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA).

[0141] The phosphor coated MOF-PVC composite was loaded into athermoforming machine. The layer was heated for 23 seconds at atemperature of 270° C. Using a plate with a circular aperture (about ½inch diameter) the phosphor coated MOF-PVC was formed into a hemisphereof about ½ inch with the phosphor on the convex side of the hemisphere.Visual inspection of the hemisphere indicated the hemisphere had agreater thickness near an outer region of the hemisphere and was thinnerat an inner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 12

[0142] A thermoformed dome of multilayer optical film (MOF) coated withzinc sulfide (ZnS) phosphor was made by the following procedure.

[0143] A sheet of MOF-PVC described in Example 11 was placed on a cleanflat surface with the MOF side facing up. The top surface of the MOF-PVCwas wiped with a lint free cotton cloth dampened with methanol. About 3grams of the ZnS phosphor paste described in Example 9 was placed ontothe MOF-PVC. The phosphor paste was hand-drawn into a coating using the2 mil gap of a square multiple clearance applicator (designated PAR-5353by BYK-Gardner USA of Columbia, Md., USA). The wet film was cured at atemperature of about 130° C. for 30 minutes in a gravity convection oven(designated Model 1350G by VWR International, Inc., of West Chester,Pa., USA).

[0144] The phosphor coated MOF-PVC composite was loaded into athermoforming machine. The layer was heated for 21 seconds at atemperature of 270° C. Using a plate with a circular aperture (about ½inch diameter) the phosphor coated MOF-PVC was formed into a hemisphereof about ½ inch with the phosphor on the convex side of the hemisphere.Visual inspection of the hemisphere indicated the hemisphere had agreater thickness near an outer region of the hemisphere and was thinnerat an inner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 13

[0145] A thermoformed dome of multilayer optical film (MOF) coated withcerium-doped yttrium aluminum gamet (YAG:Ce) phosphor was made by thefollowing procedure.

[0146] 20.01 grams of fluorpolymer resin (designated “Phosphor Ink PartA: Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035by Durel Corporation of Chandler, Ariz., USA) was placed into a 2 ounceglass jar. 19.98 grams of YAG:Ce phosphor (designated QMK58/F-U1 Lot#13235 by Phosphor Technology, Ltd. of Stevenage, England) was measuredinto a weighing dish. The phosphor was mixed into the resin by firstadding one-half of the phosphor to the resin and mixing it in by handwith a stainless steel spatula and then adding the other half and mixingit by hand. The phosphor and resin were mixed by hand until the mixturehad a smooth texture and uniform appearance. The jar containing theresulting phosphor paste was covered with a lid and placed on a bottleroller for about 30 minutes.

[0147] A sheet of MOF-PVC described in Example 11 was placed on a cleanflat surface with the MOF side facing up. The top surface of the MOF-PVCwas wiped with a lint free cotton cloth dampened with methanol. About 3grams of the YAG:Ce phosphor paste was placed onto the MOF-PVC. Thephosphor paste was hand-drawn into a coating using the 4 mil gap of asquare multiple clearance applicator (designated PAR-5353 by BYK-GardnerUSA of Columbia, Md., USA). The wet film was cured at a temperature ofabout 130° C. for 30 minutes in a gravity convection oven (designatedModel 1350G by VWR International, Inc., of West Chester, Pa., USA).

[0148] The phosphor coated MOF-PVC composite was loaded into athermoforming machine. The layer was heated for 23 seconds at atemperature of 270° C. Using a plate with a circular aperture (about ½inch diameter) the phosphor coated MOF-PVC was formed into a hemisphereof about ½ inch with the phosphor on the convex side of the hemisphere.Visual inspection of the hemisphere indicated the hemisphere had agreater thickness near an outer region of the hemisphere and was thinnerat an inner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination. Example14

[0149] A thermoformed dome of multilayer optical film (MOF) coated withcerium-doped yttrium aluminum garnet (YAG:Ce) phosphor was made by thefollowing procedure.

[0150] A sheet of MOF-PVC described in Example 11 was placed on a cleanflat surface with the MOF side facing up. The top surface of the MOF-PVCwas wiped with a lint free cotton cloth dampened with methanol. About 3grams of the YAG:Ce phosphor paste described in Example 13 was placedonto the MOF-PVC. The phosphor paste was hand-drawn into a coating usingthe 2 mil gap of a square multiple clearance applicator (designatedPAR-5353 by BYK-Gardner USA of Columbia, Md., USA). The wet film wascured at a temperature of about 130° C. for 30 minutes in a gravityconvection oven (designated Model 1350G by VWR International, Inc., ofWest Chester, Pa., USA).

[0151] The phosphor coated MOF-PVC composite was loaded into athennoforming machine. The layer was heated for 21 seconds at atemperature of 270° C. Using a plate with a circular aperture (about ½inch diameter) the phosphor coated MOF-PVC was formed into a hemisphereof about ½ inch with the phosphor on the convex side of the hemisphere.Visual inspection of the hemisphere indicated the hemisphere had agreater thickness near an outer region of the hemisphere and was thinnerat an inner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 15

[0152] A sheet of MOF-PVC described in Example 11 was heated in thethermoforming device described above to a temperature of about 270° C.for 16 seconds. This heated sheet of MOF-PVC was draped over thehemispherical lens of a commercially available 5 mm LED package withvacuum assist. The MOF-PVC acquired a final shape corresponding to thehemispherical lens shape.

[0153] The formed MOF-PVC transmission spectrum was measured using aPerkin-Elmer Lambda 19 spectrophotometer. The spectrum of the centralportion of the formed MOF-PVC was shown to have band edges at 360 nm and460 nm with a peak reflectivity occurring at 400 nm. This formed MOF-PVFhad a transmission greater than 75% at wavelengths above 500 nm. Thismeasured spectral shift of the MOF-PVC was due to the thinning of theoptical stack occurring during the shaping operation.

[0154] All patents and patent applications referenced herein areincorporated by reference in their entirety. Various modifications andalterations of this invention will be apparent to those skilled in theart without departing from the scope and spirit of this invention, andit should be understood that this invention is not limited to theillustrative embodiments set forth herein.

What is claimed is:
 1. A light source, comprising: an LED that emits excitation light; a layer of phosphor material positioned to receive the excitation light, the phosphor material emitting visible light when illuminated with the excitation light; and a non-planar flexible multilayer reflector that transmits the excitation light and reflects visible light, the non-planar flexible multilayer reflector being positioned between the LED and the layer of phosphor material.
 2. The light source according to claim 1, wherein the non-planar flexible multilayer reflector comprises polymeric material.
 3. The light source according to claim 1, wherein the non-planar flexible multilayer reflector comprises alternating layers of a first and second thermoplastic polymer and wherein at least some of the layers are birefringent.
 4. The light source according to claim 1, wherein the excitation light comprises UV light.
 5. The light source according to claim 1, wherein the non-planar flexible multilayer reflector is a concave polymeric multilayer reflector.
 6. The light source according to claim 1, wherein the non-planar flexible multilayer reflector is a hemispherical concave polymeric multilayer reflector.
 7. The light source according to claim 1, wherein the layer of phosphor material is disposed on the non-planar flexible multilayer reflector.
 8. The light source according to claim 1, wherein the non-planar flexible multilayer reflector comprises a polymeric material that resists degradation when exposed to U.V. light.
 9. The light source according to claim 2, wherein the non-planar polymeric multilayer reflector is a polymeric material substantially free of inorganic materials.
 10. The light source according to claim 1, wherein the layer of phosphor material is a discontinuous layer of phosphor material.
 11. The light source according to claim 1, wherein the layer of phosphor material is a plurality of dots of phosphor material.
 12. The light source according to claim 11, wherein each dot has an area of less than 10000 micron².
 13. The light source according to claim 11, wherein the plurality of dots comprise phosphor material that emit red, green and blue light when illuminated with excitation light.
 14. The light source according to claim 11, wherein at least a first phosphor dot emits light at a first wavelength and a second phosphor dot emits light at a second wavelength different than the first wavelength.
 15. A method of manufacturing a light source, comprising the steps of: providing a LED that emits excitation light; positioning a layer of phosphor material such that the phosphor material emits visible light when illuminated with the excitation light; and positioning a non-planar flexible multilayer reflector that transmits the excitation light onto the phosphor material and reflects visible light.
 16. The method according to claim 15, wherein the positioning a non-planar flexible multilayer reflector further comprises shaping a flexible multilayer reflector to form a non-planar flexible multilayer reflector.
 17. The method according to claim 15, further comprising thermoforming a polymeric multilayer reflector to form a non-planar flexible multilayer reflector. 